Basophils and mast cells represent an important source of several inflammatory mediators, certain of which (e.g., histamine, serotonin) are stored in the cells' cytoplasmic granules. Morphologic studies have demonstrated that basophils and/or mast cells are increased in numbers and/or exhibit activation during many different immunologic or pathologic processes in both experimental animals and man. Along with other lines of evidence, these observations indicate that basophils and mast cells participate in a wide variety of biological responses. Previous work in our laboratory has suggested that certain of the important biological functions of basophils and mast cells are mediated by a bidirectional flow of small, membrane bound cytoplasmic vesicles between the plasma membrane and the cytoplasmic granules. Such functions include the internalization of ligands bound to the cell surface, the uptake (and, later, release) of potentially toxic exogenous basic compounds, and the sustained and/or low level release of granule-associated mediators. We now wish to test this model rigorously, with an approach that utilizes a new method of microwave energy-assisted ultrafast fixation recently developed in our laboratory, as well as ultrastructural cytochemistry/immunocytochemistry, high resolution autoradiography, and computer-assisted morphometry. The role of cytoplasmic vesicles will be evaluated in the following phenomena: 1) The uptake, granule storage and release of horseradish peroxidase or eosinophil peroxidase by guinea pigs basophils and rat and mouse mast cells; (2) The stimulation of rat or mouse mast cells with gold-labeled monoclonal IgE and specific antigen, (and the relationship of such stimulation to internalization of IgE-antigen complexes); 3) The release of granule associated histamine (guinea pig basophils, and rat and mouse mast cells) and chymase (rat peritoneal cell) by various concentrations of degranulation stimuli, including IgE and antigen and certain basic compounds; 4) The uptake and release of 3H-serotonin by cloned mouse mast cells and rat peritoneal mast cells.